1. Field of the Invention
This invention relates to a process for producing an electroluminescent device (hereinafter called "EL device") to be used for a flat plate type display, various light sources and illuminations or the like and to an EL device obtained by the process.
2. Related Background Art
EL device which can emit light by application of an electrical field on a solid electroluminescent film is expected to be promising as a display device which can compete with CRT in the points that it can be made as a thin film and lightweight, that it is free from flicker and also that it can be driven at a low voltage. However, the EL devices obtained up to date are low in luminescence efficiency and also unsatisfactory in luminance. This may be considered to be due to the causes that crystallinity of the luminescent layer is poor, that scattering of electrons may be caused by impurities, etc., whereby no sufficient exitation can be accomplished.
In the method for production of EL devices known in the prior art, as the method for depositing electroluminescent films thereof (hereinafter called "EL luminescent film"), there may be included the vapor deposition method, the CVD method, the MOCVD method, the sputtering method, the ALE method (atomic layer epitaxy) method, etc., and the plasma CVD method.
The reaction process in formation of a deposited film according to the plasma CVD method which has been generalized in the prior art is considerably complicated as compared with the CVD method of the prior art, and its reaction mechanism involves not a few ambiguous points. Also, there are a large number of parameters for formation of a deposited film (for example, substrate temperature, flow rate and flow rate ratio of the introduced gases, pressure during formation, high frequency power, electrode structure, structure of the reaction vessel, speed of evacuation, plasma generating system, etc.). By use of a combination of such a large number of parameters, the plasma may sometimes become unstable state, whereby marked deleterious influences were exerted frequently on the deposited film formed. Besides, the parameters characteristic of the device must be selected for each device and therefore under the present situation it has been difficult to generalize the production conditions.
However, depending on the application use of the deposited film, bulk production with reproducibility must be attempted with full satisfaction of enlargement of area, uniformity of film thickness as well as uniformity of film quality, and therefore in formation of a deposited film according to the plasma CVD method, enormous installation investment is required for a bulk production device and also management items for such bulk production become complicated, with a width of management tolerance being narrow and the control of the device being severe. These are pointed as the problems to be improved in the future.
On the other hand, in the prior art technique according to conventional CVD method, high temperature was required and also no deposited film satisfactory on the industrial level can be necessarily obtained.
As described above, in formation of a functional film it has been strongly desired to develop a deposited film which is capable of bulk production by means of a device of low cost while ensuring practically useful characteristics and uniformness.